Textbook Question
What are two advantages of breathing air, compared with obtaining dissolved oxygen from water? What is a comparative disadvantage of breathing air?
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40. Circulatory System
Gas Exchange
3:18 minutesProblem 13
Textbook Question
Partial pressure reflects the relative amount of gas in a mixture and is measured in millimeters of mercury (mm Hg). Llamas are native to the Andes Mountains in South America. The partial pressure of O2 (abbreviated PO₂) in the atmosphere where llamas live is about half of the PO₂ at sea level. As a result, the PO₂ in the lungs of llamas is about 50 mm Hg, whereas that in human lungs at sea level is about 100 mm Hg. A dissociation curve for hemoglobin shows the percentage of saturation (the amount of O2 bound to hemoglobin) at increasing values of PO₂ As you see in the graph below, the dissociation curves for llama and human hemoglobin differ. Compare these two curves and explain how the hemoglobin of llamas is an adaptation to living where the air is 'thin.'
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Examine the dissociation curves for llama and human hemoglobin. The graph shows the percentage of hemoglobin saturation with oxygen (O2) at varying partial pressures of oxygen (PO2). The llama curve is shifted to the left compared to the human curve.
Understand the significance of the leftward shift. A leftward shift indicates that llama hemoglobin has a higher affinity for oxygen at lower PO2 levels, meaning it can bind oxygen more effectively in environments with reduced oxygen availability, such as high altitudes.
Compare the PO2 values in the lungs of llamas and humans. In llamas, the PO2 in the lungs is about 50 mm Hg, while in humans at sea level, it is about 100 mm Hg. At 50 mm Hg, llama hemoglobin is nearly fully saturated with oxygen, whereas human hemoglobin is only partially saturated at this PO2.
Relate this adaptation to the environment. Llamas live in the Andes Mountains, where the atmospheric oxygen is lower ('thin air'). Their hemoglobin's higher affinity for oxygen allows them to efficiently capture and transport oxygen even at reduced PO2 levels.
Conclude that the dissociation curve of llama hemoglobin is an evolutionary adaptation to high-altitude living. This ensures that llamas can meet their oxygen needs despite the lower availability of oxygen in their environment.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Partial Pressure of Oxygen (PO₂)
Partial pressure of oxygen (PO₂) refers to the pressure exerted by oxygen in a mixture of gases, such as the atmosphere. It is a crucial factor in determining how much oxygen is available for organisms to breathe. At higher altitudes, like the Andes where llamas live, the PO₂ is lower than at sea level, affecting oxygen availability and influencing respiratory adaptations in animals.
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Hemoglobin Saturation Curve
The hemoglobin saturation curve illustrates the relationship between the partial pressure of oxygen and the percentage of hemoglobin saturated with oxygen. This curve is sigmoidal, indicating that hemoglobin's affinity for oxygen increases as more oxygen molecules bind. The differences in the curves for llamas and humans reflect adaptations to their respective environments, with llamas showing a higher saturation at lower PO₂ levels, allowing them to efficiently extract oxygen in thin air.
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Adaptation to Altitude
Adaptation to altitude involves physiological changes that enable organisms to survive and thrive in environments with lower oxygen availability. Llamas have evolved hemoglobin that binds oxygen more effectively at lower PO₂ levels, which is essential for their survival in the high-altitude Andes. This adaptation allows them to maintain adequate oxygen transport in their blood despite the reduced atmospheric oxygen pressure.
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